Two loop control-based generalized cycle-to-cycle optimization for machining workpieces with non-circular curve in CNC grinding

摘要

In many scenarios of machining system, a workpiece with non-circular curve is manufactured by repetitively performing a given command. The size of the workpiece, however, is quite unlikely to be precisely measured until one process (or a cycle) has been completely finished. Although in-process measurement and control are possible, it is often economically prohibitive or practically complex to be conducted. To overcome this drawback, a two loop control-based generalized cycle-to-cycle (GCTC) feedback control scheme, which is an offline optimization control method, is proposed for machining workpiece with non-circular curve in this study. Inner loop is a local controller which is used to guarantee the tracking accuracy. GCTC feedback control is adopted to serve as an optimization module for the closed-loop system under the local controller to update the reference in the outer loop. The GCTC control model is developed based on the reference and measure error of the prior cycle of the machining system. The equivalent dynamic model of the machining system can be obtained by the extended state observer and repetitive control in inner loop. The sufficient stability conditions and convergence of the GCTC control are derived in this study. The proposed GCTC controllers are developed comprehensibly. The simplicity of the method lies in that only a low-pass filter and a proportional gain are required to be chosen. The superiority is demonstrated by the simulations and experiments on CNC cam grinding based on GCTC control. The application results justify the effectiveness of the GCTC scheme.